sfftc(3P) Sun Performance Library sfftc(3P)NAMEsfftc - initialize the trigonometric weight and factor tables or com‐
pute the forward Fast Fourier Transform of a real sequence.
SYNOPSIS
SUBROUTINE SFFTC(IOPT, N, SCALE, X, Y, TRIGS, IFAC, WORK, LWORK, IERR)
INTEGER IOPT, N, IFAC(*), LWORK, IERR
COMPLEX Y(*)
REAL X(*), SCALE, TRIGS(*), WORK(*)
SUBROUTINE SFFTC_64(IOPT, N, SCALE, X, Y, TRIGS, IFAC, WORK, LWORK, IERR)
INTEGER*8 IOPT, N, IFAC(*), LWORK, IERR
REAL X(*), SCALE, TRIGS(*), WORK(*)
COMPLEX Y(*)
F95 INTERFACE
SUBROUTINE FFT(IOPT, N, SCALE, X, Y, TRIGS, IFAC, WORK, [LWORK], IERR)
INTEGER*4, INTENT(IN) :: IOPT
INTEGER*4, INTENT(IN), OPTIONAL :: N, LWORK
REAL, INTENT(IN), OPTIONAL :: SCALE
REAL, INTENT(IN), DIMENSION(:) :: X
COMPLEX, INTENT(OUT), DIMENSION(:) :: Y
REAL, INTENT(INOUT), DIMENSION(:) :: TRIGS
INTEGER*4, INTENT(INOUT), DIMENSION(:) :: IFAC
REAL, INTENT(OUT), DIMENSION(:) :: WORK
INTEGER*4, INTENT(OUT) :: IERR
SUBROUTINE FFT_64(IOPT, [N], [SCALE], X, Y, TRIGS, IFAC, WORK, [LWORK], IERR)
INTEGER(8), INTENT(IN) :: IOPT
INTEGER(8), INTENT(IN), OPTIONAL :: N, LWORK
REAL, INTENT(IN), OPTIONAL :: SCALE
REAL, INTENT(IN), DIMENSION(:) :: X
COMPLEX, INTENT(OUT), DIMENSION(:) :: Y
REAL, INTENT(INOUT), DIMENSION(:) :: TRIGS
INTEGER(8), INTENT(INOUT), DIMENSION(:) :: IFAC
REAL, INTENT(OUT), DIMENSION(:) :: WORK
INTEGER(8), INTENT(OUT) :: IERR
C INTERFACE
#include <sunperf.h>
void sfftc_ (int *iopt, int *n, float *scale, float *x, complex *y,
float *trigs, int *ifac, float *work, int *lwork, int *ierr);
void sfftc_64_ (long *iopt, long *n, float *scale, float *x, complex
*y, float *trigs, long *ifac, float *work, long *lwork, long
*ierr);
PURPOSEsfftc initializes the trigonometric weight and factor tables or com‐
putes the forward Fast Fourier Transform of a real sequence as follows:
N-1
Y(k) = scale * SUM W*X(j)
j=0
where
k ranges from 0 to N-1
i = sqrt(-1)
isign = -1 for forward transform
W = exp(isign*i*j*k*2*pi/N)
In real-to-complex transform of length N, the (N/2+1) complex output
data points stored are the positive-frequency half of the spectrum of
the Discrete Fourier Transform. The other half can be obtained through
complex conjugation and therefore is not stored.
ARGUMENTS
IOPT (input)
Integer specifying the operation to be performed:
IOPT = 0 computes the trigonometric weight table and factor
table
IOPT = -1 computes forward FFT
N (input)
Integer specifying length of the input sequence X. N is most
efficient when it is a product of small primes. N >= 0.
Unchanged on exit.
SCALE (input)
Real scalar by which transform results are scaled. Unchanged
on exit. SCALE is defaulted to 1.0 for F95 INTERFACE.
X (input) On entry, X is a real array whose first N elements contain
the sequence to be transformed.
Y (output)
Complex array whose first (N/2+1) elements contain the trans‐
form results. X and Y may be the same array starting at the
same memory location, in which case the dimension of X must
be at least 2*(N/2+1). Otherwise, it is assumed that there
is no overlap between X and Y in memory.
TRIGS (input/output)
Real array of length 2*N that contains the trigonometric
weights. The weights are computed when the routine is called
with IOPT = 0 and they are used in subsequent calls when IOPT
= -1. Unchanged on exit.
IFAC (input/output)
Integer array of dimension at least 128 that contains the
factors of N. The factors are computed when the routine is
called with IOPT = 0 and they are used in subsequent calls
where IOPT = -1. Unchanged on exit.
WORK (workspace)
Real array of dimension at least N. The user can also choose
to have the routine allocate its own workspace (see LWORK).
LWORK (input)
Integer specifying workspace size. If LWORK = 0, the routine
will allocate its own workspace.
IERR (output)
On exit, integer IERR has one of the following values:
0 = normal return
-1 = IOPT is not 0 or -1
-2 = N < 0
-3 = (LWORK is not 0) and (LWORK is less than N)
-4 = memory allocation for workspace failed
SEE ALSO
fft
6 Mar 2009 sfftc(3P)
